Ultrasound Diagnostics and A-method
The main advantage of ultrasound echography in A-mode is the ability to perform precise linear measurements of intraocular structures. This is indispensable for the dynamic monitoring of neoplasm growth, controlling eyeball subatrophy, and accurately calculating the optical power of a future intraocular lens (IOL).
When interpreting a normal echogram, specialists rely on the sequence of echo signals:
- 1st peak reflects the anterior surface of the cornea.
- 2nd and 3rd peaks correspond to the anterior and posterior surfaces of the lens.
- 4th peak is formed by the retina and structures of the posterior pole of the eye.
Changes in the standard echogram occur in pathologies such as hemophthalmus, detachment of internal membranes, lens defects, neoplasms, and the presence of foreign bodies.
B-method of Echography and Combined Scans
Unlike linear distance measurement, the B-method of echography is designed for an in-depth assessment of the shape, actual dimensions, and precise topography of pathological foci within the eye structures.
Equipment for this study is equipped with a pulse echo blocker and a special device for manual or automatic movement of the ultrasound beam. A radial section of the organ under study is formed on the monitor screen. The brightness level directly depends on the reflective properties of the tissues: the higher the echogenicity of the area, the brighter the signal is visualized.
In modern clinical practice, doctors often use combined ultrasound AV-scans, which combine visualization functions and precise biometry.
Dopplerography and Laser Technologies
Dopplerography is used for the hemodynamic assessment of the visual organ. The method allows studying blood flow velocity in medium and large vessels, determining the degree of blood supply and the magnitude of pulsation.
Computerized laser scanning ophthalmoscopes made a breakthrough in detailed diagnostics. Historically, the first topographic system appeared in 1986. Today, devices scan the surface of the retina, building its visual three-dimensional (3D) model.
Clear examples of such equipment are the Optical Coherence Tomometer (OCT) and the Heidelberg Retinal Tomograph (HRT). They are indispensable in glaucoma, assessing optic disc excavation (OD), measuring nerve fiber thickness, and performing flowmetry to analyze blood flow.
We remember the echogram peaks from front to back: Cornea (1) -> Lens on both sides (2 and 3) -> Retina and posterior pole (4).
Class and exam questions
What is the main diagnostic advantage of A-scanning in ophthalmology?
The main advantage of the A-method lies in the ability to accurately measure intraocular distances (biometry), which is necessary for calculating the optical power of the intraocular lens (IOL), as well as for monitoring neoplasms and eye subatrophy.
What is the fundamental difference between the B-method of echography and the A-method?
The A-method is designed for precise linear measurement of distances and analysis of echogenic peaks. The B-method is used for a more complex assessment of the shape, size, and topography of a pathological focus with the formation of a radial section of the eye on the screen.
Which structures correspond to the peaks on a normal echogram during A-scanning?
The first peak is the anterior surface of the cornea, the second and third peaks are the anterior and posterior surfaces of the lens, and the fourth peak is the retina and structures of the posterior pole of the eye.
What are laser scanning ophthalmoscopes used for?
They create 3D retinal models, assess the state of the optic disc in glaucoma, measure the thickness of the nerve fiber layer, and also allow flowmetry and retinal vessel angiography.
What else to study on this topic
- Dynamic monitoring of glaucoma patients using HRT and OCT
- Assessment of optic disc excavation and nerve fiber layer thickness
- Flowmetry and angiography (fluorescein and indocyanine)
- Electroretinography (ERG) as a method for assessing the functional state of the retina
- Study of the rod and cone apparatus of the retina, as well as the pigment epithelium
Master the entire topic in the "Diagnostic Radiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Biometry in Ophthalmology" and 2,199 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 10 video lessons on the subject
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.